(1) A PZT Film by a Sol-Gel Method
A PZT film formed by a sol-gel method is conventionally known. However, the PZT film has following drawbacks.
Since Pb has a high vapor pressure, Pb comes out easily from the PZT film. As the result, according to the principle of electric charge neutrality, an oxygen ion deficiency is large, a leak current density is larger than 10−6 A/cm2, and the film is a porous film containing large amount of air bubbles, and furthermore, in the case of a thick film of 1 μm or more used for MEMS, the film has black color and has lost interference color. Moreover, in a sol-gel method by spin coating, when a thick PZT film of 1 μm or more is to be fabricated, cracks appear easily due to a large residual stress of the thick PZT film. In addition, in a film forming method of a PZT film by a sol-gel method, the process time becomes long due to stacking of 20 layers or more.
(2) A PZT Film by a Sputtering Method (for Example, See Patent Document 1)
Patent Document 1 discloses a PZT film formed by a sputtering method. The PZT film has advantages such as a small leak current density, capability of epitaxial growth and high initial properties.
But, the PZT film has following drawbacks.
Since the PZT film is exposed to plasma during the film formation, it is damaged easily by ions etc., the PZT film is imprinted, or the hysteresis is deformed and properties are likely to be deteriorated. Since an epitaxial growth proceeds slowly, the film forming time is as long as several hours. Furthermore, since the manufacturing apparatus makes use of a high vacuum and high temperature, the cost becomes high and the product unit price cannot be lowered. Moreover, since the formation of uniform plasma in the film forming is difficult, the variation of film properties and film thickness of the PZT film becomes large to make mass productivity poor.
Especially when a sputtering method is employed for mass production, variation of the composition, thickness and various properties of PZT films are large due to the influence of erosion.
(3) A PZTN Film (for Example, See Patent Document 2)
Patent Document 2 discloses a ferroelectric film including a perovskite-structured ferroelectric substance represented by ABO3, the disclosure being a PZTN ferroelectric film in which the perovskite-structured ferroelectric substance is a PZT-based ferroelectric substance containing Pb2+ as A-site ions and containing Zr4+ and Ti4+ as B-site ions, and containing Si2+ in the A-site as A-site compensation ions and containing Nb5+ in the B-site as B-site compensation ions.
But, the PZTN ferroelectric film has following drawbacks.
Since it contains Si2+ in the A-site as A-site compensation ions, the ferroelectricity is deteriorated largely by the Si (see FIG. 5). Although it contains Si2+ in the A-site as A-site compensation ions and Nb5+ in the B-site as B-site compensation ions, Si and Nb can not sufficiently prevent the deficiency of an oxygen ion, or not sufficiently suppress the leak current. Furthermore, when making a PZTN ferroelectric film thick, a thick film is obtained, by a sol-gel method, through the use of a sol-gel solution having a large contact angle (for example, 60° or more). Therefore, air bubbles enter easily into the PZTN ferroelectric film.